Aliphatic tertiary amines are useful as corrosion inhibitors, urethane catalysts and oil additives. They are also useful as intermediates for the production of quaternary ammonium salts and amphoteric surface active agents such as disinfectants, fungicides, sanitary agents, retarders in dyeing, and antistatic agents. As the use of aliphatic tertiary amines is continuing to expand, the requirements for their quality as intermediates are becoming increasingly stringent. Among other things, tertiary amines are required to be color stable and odorless. Accordingly, impurities that may impart undesired colors or smells to the final product must be kept at low levels.
Various prior art methods for the reductive alkylation of polyamines to prepare tertiary amines are well known. However, in the prior art methods, excess solvent has to be used in order to prevent the reaction mixture of amine-formaldehyde and solvent from gelling or forming a solid. This is particularly true when reductively alkylating a polyamine having at least two primary amino groups. The solvent then has to be removed from the final product. Finally, this solvent has to be disposed of properly, which can be costly. Further, due to the presence of large amounts of solvent, the yields on a per batch basis are decreased because more of the crude reaction effluent is solvent rather than product.
EP 0142868 discloses a process for producing a tertiary amine by alkylating a specific amine, including certain polyamines, with a carbonyl compound, e.g., formaldehyde, in the presence of a hydrogenation catalyst while continuously supplying the carbonyl compound to the reaction zone. However, the specific amine thereof is not a polyamine having at least two primary amino groups. Further, the hydrogenation catalyst must have at least one of Co, Ni, Ru, Rh, Pd or Pt supported on pulverized or granular carbon. Other supports or catalysts were not suitable for providing a color stable and odorless product.
Accordingly, there is a need for a method of reductive alkylation of polyamines having at least two primary amino groups which does not require excess solvent and produces a color stable and odorless product. Further, there is a need for a method of reductive alkylation of polyamines using catalysts which are not supported on carbon.